https://www.hackerrank.com/skills-verification/sql_basic Hackerrank could be a good option! Plenty of practice exercises for you to do. The link above is the beginner certification. There are two others, if I'm not mistaken. Every certificate is totally for free. If you're looking for dedicated SQL courses, I'd look on YouTube. While I haven't tried it, Alex the Analyst's free bootcamp seems pretty solid and gives a great foundation. When you feel more comfortable, I'd recommend creating your own databases and tables using a tool like MySQLWorkBench (but you could really use anything, honestly). Just be sure to read the documentation, follow along some free tutorials and get to the point where you can define, design and develop your own end-to-end projects. That's hands down the best way to learn pretty much anything. Best of luck!! More on reddit.com

I recommend Codecademy, I’m currently going through their “Analyzing Data with SQL” pro path and intend on going through their “Design Databases with PostgreSQL” I’m learning basic queries, aggregates, how to setup PostGreSQL and create databases right now. They also offer additional SQL training like “How to analyze business metrics with SQL” and give you access to some of the big BI tools like Power BI and Tableau. They provide a certificate at the end of it but I’m not sure how much if any weight it carries career wise, but I’ve the training extremely helpful in my new role as a financial systems analyst. More on reddit.com

https://sqlbolt.com is great to get acquainted with the basic syntax. Don't make it a challenge though. If you get stuck just check the answer, fill in the answer (muscle memory) and come back later to see if you can remember it. The reason you should be rushing through this fast without any concern whether you understand it or not is because you'll learn SQL faster if you learn it top-down. Which means exploring the problem first, establishing how it needs to be broken down, and then finally at the end enter the syntax. And that's when job interview problems (start anywhere on Youtube) are awesome, they're all derived from real world databases. They all will walk you through this process the right way. People who start trying to get a perfect syntax first will be treading water for a long time before they get to chew on what makes SQL so satisfying to work it. That's what I did and I wish someone had told me this. Instead I had SQL for Dummies starting me out on database sanitation... More on reddit.com

LearnSQL.com. They have a complete SQL learning path that takes you from the basics to advanced topics like window functions and CTE. They have courses in different dialects: standard, SQL Server, MySQL, and others. They have a lot of practice courses. When it comes to SQL, it’s the most complete learning platform. More on reddit.com